The pheromone response pathway in the yeast Saccharomyces cerevisiae provides a genetically advantageous system to understand how extracellular signals result in changes in gene expression. Our work has shown that the STE12 protein is a critical target of this response pathway in both of the haploid cell types, a and alpha. STE12 binds to the pheromone response element, the DNA sequence mediating increased transcription of a-specific genes in response to treatment with the pheromone alpha-factor, and of haploid-specific genes in response to treatment with alpha-factor or a-factor. STE12 becomes rapidly phosphorylated in pheromone-treated cells, and this modification correlates with transcriptional activation. In addition, we have characterized the DNA-binding domain of STE12 and shown that it possesses certain similarities to the homeodomain, although it is highly divergent. Our overall goals for this grant period are to understand more clearly how the signal generated by pheromone treatment leads to increases in transcription. Specifically, we plan: 1)To further define the DNA-binding domain of STE12 and the repertoire of DNA sequences to which this domain binds. 2)To analyze the phosphorylation of STE12 under pheromone-inducing and non-inducing conditions, and to try to determine how this modification affects transcriptional activity. 3)To understand the role of STE12 in the transcription of alpha-specific genes, in which the sequence mediating a-factor induction does not directly bind STE12.